Pipe joint connections of various types are well known for gripping pipe and forming couplings. Pipe joint glands, for example, have long been used to couple a plain or spigot end of pipe, such as water main, to a mechanical joint bell end of an adjacent pipe section or mechanical joint fittings, valves and hydrants (sometimes hereinafter, "attachments"). The bell end typically features an annular flange which contains a number of bolt holes. The bell end also typically contains a recess into which a portion of the spigot end of adjoining pipe fits. A pipe joint gland, which features an annular flange having bolt holes that correspond to the bolt holes in the adjoining bell end flange, is placed about the spigot end.
Pipe joint connections also feature means for gripping the pipe to retain it: in position against the next fitting, pipe, valve or hydrant. Frequently such connections contain set screws for this purpose. Such set screws penetrate the connection in a direction generally perpendicular to the pipe axis to fasten the connection to the pipe.
A second gripping mechanism, commonly employed in glands (with or without use of set screws), is a sealing ring disposed in the bell end against which a contact face of the gland impinges. When the bolts connecting the bell end and the gland are torqued appropriately, the gland impinges on the sealing ring to force the ring against the spigot end and into the bell end in order to help form a fluid-tight seal and to grip the spigot end of the pipe. Such glands are shown in U.S. Pat. No. 4,544,188 issued Oct. 1, 1985 to Dugger which is incorporated herein by reference.
Mechanical joint pipe connections which use set screws typically entail certain disadvantages. First, the set screws typically feature a pointed or hollow-conical foot which can scar the pipe and which can create point stresses and thus eventual failure sites on the pipe. Second, conventional set screws rigidly attach the pipe to the connection and thus form a rigid coupling. Such rigidity is frequently undesirable for pipes placed in the earth, which require a degree of flexibility. Additionally, because of this rigid structure, the coupling has no ability to flex and adjust itself over time in order to maintain constant gripping power despite changes in temperature, pressure and other factors which can affect expansion and contraction of the pipe, set screws and connection.